As if air travel weren’t annoying enough, new research suggests that global warming will force planes to carry fewer passengers to get off the ground. While a little more legroom might sound good, it could make flying more expensive.

Researchers examined the impact of rising temperatures on five types of commercial planes flying out of 19 of the world’s busiest airports. In the coming decades, 10 to 30 percent of flights that take off during the hottest time of day could face weight restrictions, they found.

That’s because warmer air particles are more spread out, so they generate less lift under a plane’s wings as it barrels down the runway. As a result, a plane must be lighter to take off. In some cases, a typical 160-seat plane would have to jettison 4 percent of its weight — say, a dozen passengers, the researchers calculated.